A Step-Wise Method for Measuring Thermophysical Parameters of an Isotropic Material, Considering the Effect of Thermal Contact Resistance and Lateral Convection Losses

Abstract

This work proposes a model based on the step-wise method to identify conductivity and heat capacity. Contrary to conventional models, this model considers the thermal properties of the heating element, the thermal contact resistance at the measurement point, and the lateral convection losses around the device. The mathematical model is solved using a numerical approach based on the finite element method (FEM) to obtain the temperature distribution over the entire measurement device. This temperature field is generated by the passage of electric current through a flat electrical resistor made of thin metal foil (Kapton). Heat is produced as a progressive function. A thermocouple placed at a distance from the heat source measures the temperature response. A sensitivity analysis showed that the heating element parameters did not affect the long-term estimates. Additionally, this sensitivity analysis showed the possibility of estimating conductivity, heat capacity, contact resistance, and convection coefficient. Experimental data obtained with this model on two materials are compared with results obtained using conventional methods (HotDisk TPS2200, fluxmeter). There is a 2.5% difference between the thermal conductivities obtained with our model and the HotDisk and fluxmeter methods. The maximum relative error in thermal capacity is 6%.